Edwin van der Sar admitted Ajax wanted to keep hold of Erik ten Hag but couldn't stop their manager from joining "one of the biggest clubs in the world".
Manchester United have confirmed the appointment of Ten Hag on a three-year deal, with the option of a further year, and he will take over at Old Trafford this summer.
The 52-year-old has spent the last four-and-a-half seasons at Ajax and is on course to win a third league title this season, although their hopes of a double were ended by PSV Eindhoven in Sunday's cup final.
READ MORE: Ten Hag announced as next United manager
Ajax were also joint top of the league when the 2019/20 season was curtailed due to the pandemic and Ten Hag has taken the club back to the pinnacle of the domestic game.
He also took them to the semi-finals of the Champions League in 2018/19, the first time they had reached that stage of the competition in 22 years.
They came within seconds of reaching the final that season but once that team had been broken up Ten Hag built another impressive side that won all six of their group games this season before falling to a surprise defeat to Benfica in the last-16.
Van der Sar wants Ten Hag to sign off with that third title but said the club already owes him for the success he has bought to Amsterdam.
"Four and a half years is a good amount of time, but we would have liked to have kept Erik at Ajax for longer. He is going to make the step to one of the biggest clubs in the world, in a fantastic league," he said.
"We owe Erik a lot of thanks for what he has achieved with Ajax so far, but we are not done yet. At the end of the season, I will look back more extensively on his departure. For now, what matters is the final games of the season in which we all want to bring home the league title."
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